Late Cretaceous and Cenozoic denudation of northern Central Vietnam examined through apatite fission track analysis

Abstract

Tectonism is associated with uplift and exhumation but are commonly difficult to decipher due to large gaps in the stratigraphic record. Northern Central Vietnam has a highly dynamic exhumation and tectonic history affected by Middle Paleozoic and latest Permian to Triassic orogenies but also less known younger events. We explore this history through analysis of apatite fission tracks (AFT) together with stratigraphy and vitrinite reflectance, seismic data and new U/Pb zircon-ages. Late Cretaceous and Paleocene uplift and exhumation are here attributed to a poorly understood orogenic event. It was followed by mid- to Late Cenozoic doming and rift pulses and intervening periods of subsidence and basin development associated with regional SE Asian tectonism and establishment of South China Sea basins.

We document the evolution of NW-striking structural lineaments in northern Central Vietnam and their repeated reactivation. The complex Central Vietnamese fault block mosaic formed since the Paleozoic during different tectonic events associated with movements over these structural lineaments. Fault blocks were exhumed during Late Cretaceous and Cenozoic uplift phases, recorded by AFT in four discrete thermotectonic episodes around 82–70, 61–59, 43–42, and 19–15 Ma. The NW-striking crustal lineaments controlled deformation and uplift during Middle Paleozoic, latest Permian to Triassic and Late Cretaceous to Early Cenozoic orogenies. While the two former orogenies are well-known, the latter is poorly realized despite its super-regional nature across Indochina and SE China. It may relate to plate collision and the cessation of Paleo-Pacific subduction underneath SE Asia. Between the orogenic episodes, rifting reactivated the NW-striking crustal lineaments in the Carboniferous-Permian, Late Triassic and mid-Cenozoic causing basin development in Central Vietnam and neighboring areas. The mid-Cenozoic event led to the opening of the Hue Sub-basin at the Gulf of Tonkin margin. Uplift and one to one-and-a-half kilometer post-rift erosion sourced sediments to this sub-basin, including Upper Miocene petroleum reservoir sands.